1. Field of the Invention
This invention relates to an electroplating method, and more precisely, to a method for electroplating in a single electroplating bath comprising varying the plating conditions so that a non-magnetic plated film and a ferromagnetic plated film are selectively deposited.
2. Description of the Prior Art
In conventional memory elements having a ferromagnetic thin film, some elements are composed of a ferromagnetic film deposited on a non-magnetic base and other elements additionally have a protective non-magnetic film superplated on the ferromagnetic film. Representative examples of such memory elements are magnetic discs for video slow-motion and for stationary image reproduction, and magnetic heads.
Conventional processes for producing these elements having a non-magnetic film and a ferromagnetic film include the following steps.
In the step for forming a non-magnetic film, a non-magnetic plating bath (such as a copper plating bath, a zinc plating bath, a chromium plating bath or a gold plating bath) is used, and thereafter a non-magnetic plated film is formed using this non-magnetic plating bath. Analogously, in the step for forming a ferromagnetic plated film, a ferromagnetic plating bath (such as a nickel plating bath, a cobalt plating bath or a nickel-cobalt alloy plating bath) is used, and thereafter a ferromagnetic plated film is formed.
However, these conventional plating processes have the following defects.
1. For obtaining a non-magnetic plated film and a ferromagnetic plated film, plural plating baths, each corresponding to the films to be formed, are necessary, that is, a plurality of plating baths are required.
2. In any of the processes comprising a non-magnetic plating step followed by a ferromagnetic plating step or vice-versa, the article to be plated must be transferred from a first plating bath to a second plating bath. Accordingly, unneeded apparatus for transferring the article and loss of plating time are inevitable.
3. A washing step with water is necessary each time when the plating is carried out in a different plating bath for the purpose of preventing intermixing of one plating solution in the other plating bath, and much time is required to complete the entire plating procedure.
U.S. Pat. No. 2,453,668 Marisic et al discloses an electrodeposition process for removing pin-holes to improve the luster of an electrodeposited film. There is no description in the patent of a plating method which enables one to obtain magnetic or non-magnetic properties in an electrodeposited film.
British Pat. No. 1,136,491 discloses electroplating magnetic film at, for example, a current density of 0.68A/dm.sup.2.
British Pat. No. 1,210,270 discloses that the composition of an electroplated layer can be altered by changing plating conditions.
French Pat. No. 2,007,304 discloses, inter alia, a process for forming a permalloy magnetic layer having a low Hc value.
As described above, these conventional plating processes have numerous defects. In an effort to overcome these defects, extensive investigation of the various fundamental phenomena in electroplating has been conducted and the present invention has been achieved.